1. Field of the Invention
The present invention relates generally to a method and system for supporting Internet Protocol (IP) mobility of a mobile node in a mobile communication system. More particularly, the present invention relates to a method and system for supporting IP mobility of a mobile node using Mobile IP (MIP) and Session Initiation Protocol (SIP) by means of a home address.
2. Description of the Related Art
The support of Internet Protocol (IP) mobility of a Mobile Node (MN) is based on technology by which the MN can receive a packet from a Correspondent Node (CN) without communication cut-off even when it moves outside a home network and is assigned a new IP address in an IP-based packet communication network.
The IP mobility of the MN has been conventionally supported by Mobile IP (MIP) technology defined by the Internet Engineering Task Force (IETF).
FIG. 1 illustrates a conventional packet communication network supporting Mobile Internet Protocol (MIP) and Session Initiation Protocol (SIP).
Referring to FIG. 1, MIP technology supports IP mobility in environments in which a Home Agent (HA) 122 and Foreign Agents (As) 141a and 141b manage a home network 120 and foreign networks 140a and 140b, and Mobile Nodes (MSN) 142a and 142b based on the MIP technology move within a system.
The MNs 142a and 142b have home addresses serving as unique IP addresses assigned by their home network 120. For example, when moving to the new foreign networks 140a and 140b, the MNs 142a and 142b receive Care-of Addresses (CoAS) serving as new IP addresses assigned by the FAs 141a and 141b and register the received assigned CoAs in the HA 122 such that they receive packets from the foreign networks 140a and 140b. In this case, a Correspondent Node (CN) 110 always sends packets to the home addresses of the MNs 142a and 142b, regardless of changed locations of the MNs 142a and 142b. 
A packet in which the home address of the MN 142a or 142b is recorded is delivered to the home network 120. The HA 122 then intercepts the packet directed to the home address of the MN 142a or 142b and delivers the intercepted packet to the current CoA of the MN 142a or 142b through IP encapsulation. Accordingly, even when the MN 142a or 142b using the MIP technology moves to a new location, it can maintain seamless packet communication through its unique home address.
As a signaling protocol for processing a multimedia call in an IP-based packet communication network, Session Initiation Protocol (SIP) is adopted and widely used as the standard. The SIP is a protocol for exchanging a control signal to generate and release a multimedia call. Because the number of users desiring to receive an IP multimedia service during movement is increasing, a large amount of research is being performed on technology for supporting IP mobility of MNs by extending the SIP without using a special mobility support protocol.
When the MN using the SIP exits the home network and moves to a foreign network, new location information is registered in a SIP proxy server. Accordingly, after the MN moves to a new location, the SIP proxy server informs the CN of MN location information, such that a SIP call can be established between the CN and the MN. When the location of the MN is changed while communication is in progress, the CN can send a packet to a new location of the MN if the MN sends a new IP address, indicating the changed location, recorded in a contact field of a SIP re-invite message header.
However, even when the location of the MN is changed, the SIP takes into account only a state in which the location of the MN is fixed while a multimedia call is established. Accordingly, the SIP can support the IP mobility while the MN does not perform a communication function, but has a limitation in supporting IP mobility while the MN performs communication. That is, when the MN moves to a new foreign network while communication is in progress and is assigned a new IP address in addition to a previous IP address, it is difficult for a call in progress to be reestablished after an additional control signal is exchanged such that a connection-based call in a Transmission Control Protocol (TCP) layer higher than an IP layer is supported. Moreover, it is difficult for a special TCP monitoring agent to be implemented in the MN and the CN.
Therefore, it is predicted that most of the MNs will use both the MIP for IP mobility and the SIP for processing an IP multimedia call in the next generation packet communication network. In this case, when the MN moves to a new location from the network and is assigned a new IP address, a location registration process is performed in the MIP and subsequently a location registration process is additionally performed in the SIP. Accordingly, there is a problem in that the location registration process must be repeatedly performed. When mobility of the MN is high and a connection point on the network is frequently changed, there are other problems in that battery power consumption of the MN is high due to the frequent location registration process, and limited wireless resources are inefficiently used because control signaling increases in a wireless zone of a wireless packet communication system.
FIG. 2 is a flow chart illustrating operation of a MN using both MIP and SIP.
When the MN receives applied electric power or moves to a new location, it receives an agent advertisement message from a Foreign Agent (FA) in step 201. The MN is assigned a new CoA through MIP location registration and registers the new CoA in a Home Agent (HA) in step 202. When the MIP location registration is terminated, the MN performs a SIP location registration process in step 203, and waits in a standby state in step 204. When receiving a SIP invite message from a CN through a SIP proxy server in step 204, the MN sends a SIP response OK message in step 205. The CoA indicates that the current location of the MN is recorded in a contact field of the SIP response OK message.
Subsequently, when a SIP call is established between the MN and the CN, a packet is transmitted and received in step 206. When the SIP call is terminated, the MN returns to the standby state in step 204. However, when the MN moves to a new location and a handover is performed while packet communication is in progress, that is, the SIP call is in progress, in step 206, the MN receives an agent advertisement message from a FA in step 207, and is assigned a new CoA through the MIP location registration process in step 208. The MN registers its own location in a MIP based HA. After the MIP location registration, the MN sends a SIP re-invite message to the CN, informs the CN of the new CoA, and continuously exchanges a packet of the SIP call in progress with the CN in step 209.
After sending the SIP re-invite message to the CN, the MN performs a special SIP location registration process in the SIP proxy server.
FIG. 3 is a flow chart illustrating a process in which an MN is assigned a new IP address and registers a new location when moving to a foreign network outside a home network in the conventional packet communication network.
When the MN exits the home network and moves to the foreign network, it receives an agent advertisement message periodically broadcast by a FA A located in the foreign network in step 301. Subsequently, the MN is assigned a new CoA serving as a new IP address to be used in the foreign network and makes a location registration request by sending a MIP registration request message to the FA A in step 302.
In step 303, the FA A sends the MIP registration request message to a HA and makes a request for location registration of the MN. Accordingly, the HA stores the new CoA of the MN and then sends a MIP registration reply message to the FA A in step 304. Subsequently, the FA A delivers the MIP registration reply message to the MN in step 305.
When the MIP location registration process is terminated, the MN performs a SIP location registration process to inform a SIP proxy server of the new CoA to be used to receive a packet. That is, the MN requests that the SIP proxy server register the current location of the MN through a SIP registration message in step 306. Then, the SIP proxy server stores location information of the MN and indicates that the SIP location registration process is successful through a SIP response OK message in step 307.
FIGS. 4A and 4B illustrate the structures of conventional databases for storing subscriber-by-subscriber location information in a MIP based HA and a SIP proxy server.
As illustrated in FIG. 4A, subscriber-by-subscriber location information in the MIP-based HA is managed in the form of a table including an MN's home address, a CoA and a valid lifetime or duration of the CoA. As illustrated in FIG. 4B, a SIP user Identification or Identifier (ID) and a CoA serving as current location information of a user reported to the SIP proxy server when SIP location registration is performed are recorded as subscriber-by-subscriber location information in the SIP proxy server.
FIG. 5 is a flow chart illustrating a conventional process for establishing a SIP call from a CN to an MN.
In step 501, the CN sends a SIP invite message to a SIP proxy server in order to establish the SIP call directed to the MN with which the CN desires to communicate. In step 502, the SIP proxy server delivers the SIP invite message to a CoA of the MN registered in the SIP proxy server. In step 503, the MN sends a SIP response OK message to the SIP proxy server when receiving the SIP invite message. In step 504, the SIP proxy server sends the SIP response OK message to the CN. At this point, the MN records the CoA of the MN in a contact field of a header of the SIP response OK message such that the CN can identify the current location of the MN from the SIP response OK message. Through the above-mentioned process, the SIP call is established between the CN and the MN, such that the CN and the MN can transmit and receive a packet without intervention of an agent.
FIG. 6 is a flow chart illustrating a conventional process for supporting mobility of a MN when a call is transferred from a foreign network A to a foreign network B while the MN maintains the call in progress.
In steps 601 to 605, when the MN moves from the foreign network A to the foreign network B, it receives an agent advertisement message periodically broadcast by a FA B and performs a MIP location registration process in the FA B. Steps 601 to 605 illustrated in FIG. 6 are identical with steps 301 to 305 illustrated in FIG. 3. Accordingly, a description of steps 601 to 605 will be omitted. When the MIP location registration process is terminated, the MN sends a SIP re-invite message and informs a CN of a new CoA serving as new location information of the MN in step 606. The CN sends a SIP response OK message to the MN such that packet transmission and reception associated with a SIP call in progress can be maintained through the new address in step 607.
After a handover operation on the call in progress is performed through the above-described process, the MN performs a location registration process in a SIP proxy server through a special signaling process and registers the new location information in steps 608 and 609.
When the MN using both the MIP and SIP moves to a new location and is assigned a new IP address, it must register the new location information in a MIP-based HA and the SIP proxy server if the MN maintains the conventional MIP and SIP. In this case, there is a problem in that many control messages for location registration must be exchanged. In the conventional method, content registered in the MIP-based HA and content registered in the SIP proxy server all are pertain to the current location information of the MN. Accordingly, there is a problem in that double location registration processes are unnecessarily performed and hence wireless resources are inefficiently used.
When the MN separately performs MIP location registration and SIP location registration according to the prior art, there is an advantage in that a call setup process is simple and its delay is short because both the MIP-based HA and the SIP proxy server can identify the current location of the MN. However, when location registration is frequently performed because mobility of the MN is high, the double location registration processes are ineffective in terms of the MN and the network. More specially, there is a serious problem in that the location registration process is complex when a call is handed over to a new network while the MN maintains the call in progress.